DAMAGE IN AEROBIC AND ANAEROBIC SYSTEMS 



27 



the same as if water (~ K) per cent in the embryo) had been present 

 dnring irradiation. 



If. however, the water used for hydration contains dissolved oxygen 

 (at or beU)w 300/liM/I), greater damage is observed. Evidently, if the 

 oxygen and the water enter the embryo simiUtaneously, the oxygen 

 competes successfully for long lived radicals, as it does in all cells of 

 normal (high) water content. 



It was observed by Caldecott that after thermal annealing for 15 min 

 at 85°C the long-lived intermediates induced by the irradiation of dry 

 seed are no longer responsive to the presence or absence of oxygen in 

 the water in which the seed is soaked. In this respect also the seed 

 closely resembles dry spores, since it was found by Powers that ther- 

 mal annealing eliminated the post -irradiation effect of oxygen. 



In this connection the interesting observation has been made by 



4 8 12 16 



Percentage H2O 



Fig. 1. — Influence of oxygen, nitric oxide and humidity on radiation damage to seeds. 

 (Redrawn, by paraiission, from Sparrman el al., 1959). 



Caldecott (1960) that, whereas the yield of interchanges observed at 

 meiosis in barley plants grown from irradiated dry seed increased 

 linearly with dose when the seeds were irradiated and soaked anoxically : 



Exchanges = 1-94Z) 



Seeds which were irradiated and soaked in aerated water gave a yield of 

 exchanges which contained an additional term in (Dose)^: 



Exchanges = l-76i)-f0-31i)2 



